In machining metallic work pieces, an apparatus called a tap is used to create internally threaded holes for receiving screws in the metallic work pieces. The tap itself is a tool with external cutting threads. In order to create the internally threaded hole in the work piece, the tap is rotated and driven into the work piece to the desired hole depth, and then once the tap reaches the desired depth, the rotation of the tap driver and consequently the tap is reversed and the tap is retracted from the base material or work piece.
The tap is held by a what is referred to as a tap driver, tapping apparatus or tapping system, and the tap driver is held or secured within a machine. There are generally two types of tapping systems, namely those wherein the reversing of the tap attachment is provided by the machine which is driving the rotation of the tap, and those systems wherein the tap attachment itself provides the reversal of the rotation. The latter are generally referred to as self-reversing.
With taps that may be rotated at three thousand (3,000) to six thousand (6,000) revolutions per minute (“rpms”), the quick stopping of the forward rotation and the immediate reversal of the direction of the rotation creates stresses. Furthermore, a portion of the self-reversing taps utilized axial movement of components within the tap body in order to initiate or facilitate the reversal in rotation of the drive spindle, and consequently the chuck which holds the tap, as well as the tap.
Tapping also normally requires the lubrication of, or the providing of coolant to, the tap and/or hole being tapped. The general types of coolant systems are referred to as internal coolant systems and/or external coolant systems. The external tap coolant systems generally include the spraying of coolant and/or lubricant on the workpiece and/or tap itself to provide sufficient or desired coolant to the hole being tapped. In a typical embodiment of this approach, a significant amount of coolant is flooded in the area. The internal tap coolant systems generally provide high pressure coolant to the tap area through passageways in the tapping attachment, which generally outlet at or near where the tap is held to the tap body (this may also be referred to as the chuck or chuck portion).
There are different types of devices and mechanisms which provide internal coolant systems, and one such type is referred to as a balanced coolant system. In many or all of the self-reversing taps, the drive spindle moves axially as it engages and/or disengages the reverse and forward rotation configurations, and the forces around the reciprocating parts or components within the tapping attachment should be maintained to prevent the undesired or untimely axial or reciprocating movement of those components.
If the high pressure coolant were merely introduced through the tap attachment and to the area where the tap is attached, it may tend to cause the axial movement of the drive spindle and other components when such movement is not desired. In order to reduce or avoid this type of undesirable axial movement, the high pressure coolant is routed on two sides of some components and/or distributed so that the pressure on the respective parts and/or surfaces is balanced and does not cause undesired axial movement of internal components such as the drive spindle.
As background for some aspects of the invention and to show alternative components which may be used in other aspects of the invention, examples of prior self-reversing tapping attachment patents include: U.S. Pat. Nos. 3,999,642; 4,002,348; 4,014,421; 4,566,829; 4,705,437; 4,832,542; 5,174,424; 5,195,624; 5,203,651; 5,209,616; 5,213,413; and 5,628,593, all of which are hereby incorporated herein by this reference. The aforesaid patents and application disclose and claim tapping attachments.
Prior patents and devices include a tap holding spindle and simultaneous rotation of forward and reverse drivers, the spindle being freely floating and moveable axially with respect to the forward and reverse drivers. Under forward drive in which the tap holder spindle is driven by the forward driver, the tap threads a hole being tapped in the workpiece and thereby screws itself into the hole. Upon cessation of feed by the driving machine with retraction of the driving machine, relative axial movement results between the tap holding spindle and the driver members such that the forward drive member becomes disengaged from the tap spindle, which at this point is held relatively stationary due to the fact that the tap has become fastened to the workpiece. Upon further retraction movement by the tapping machine and further relative movement, the reverse drive member becomes engaged with the tap holding spindle, causing reverse rotation thereof and thereby unscrewing the tap from the hole. In this manner, self-reversing by the tapping attachment itself as opposed to reversing by the driving machine, is accomplished.
With the advent of Computer Numeric Control (CNC) machining centers, self-reversing has become of greater and greater importance in that it causes reversing to occur in the tapping attachment, as opposed to requiring the driving machine to reverse its direction of rotation.
Self-reversing tapping attachments have particular parts, which due to the very nature of self-reversing suffer greater stress and wear than other parts, especially in connection with modern ultra-high-speed tapping. A portion of such stress and wear may primarily occur in the transition between forward and reverse, wherein the balls in the coupling on the tap holding spindle proceed through a limited neutral zone between engagement with splines on the forward drive element and splines on the reverse drive element. The mass of the components that are rotating in the forward direction and need to be reversed impacts the wear, operation and expense of these tapping attachments.
It is also desirable in self-reversing taps or tapping attachments, to minimize the mass of components which reverse directions with the drive spindle, due to numerous obvious and/or known concerns.
In tapping attachments which include both rotational and axial movement of the drive spindle, it is also more difficult to provide a sealed conduit, passageway and/or lubricated cavity when the seal must be provided in an environment wherein there is both rotational and axial movement. In most sealing applications for higher pressure coolant or fluid, it is normally preferred at one location or interface to only provide sealing for either rotational movement or for axial movement, but not for both at the same location or seal.
Known prior self-reversing tapping attachments, which also include a coolant system, typically integrate most or all of the cooling system components and sealing components into the drive spindle and/or tap attachment body such that when excessive wear occurs, the entire tap attachment is replaced.
In addition to the high pressure coolant passageways, conduits and lubricated cavity areas, there is also one or more internal cavities within the tap attachments, and said passageways, conduits and lubricated cavity areas are preferably operated without coolant therein. However there are multiple ways that coolant can get into the internal cavity, from the high pressure coolant areas and/or from the exterior (such as from a pumping or sucking action of the seals when the tap attachment is moving axially). It is undesirable to allow coolant to collect in or fill the internal body cavity of the tap attachment, although it tends to happen in most applications. If the non-high pressure cavity collects an undesirable amount of coolant, it can alter the operation of the tap attachment in several ways, such as altering the location of the tap itself so that inaccuracies or failures occur.
It is therefore an object of some embodiments of this invention to provide an improved self-reversing tapping or tap attachment.
It is a further object of some embodiments of this invention to provide a coolant system for use in a tapping apparatus or tapping system which does not reverse rotation with the drive spindle.
It is a further object of some embodiments of this invention to provide a modular coolant system which may be attached or detached from the remainder of the tapping attachment.
It is a further object of some embodiments of this invention to provide a tap attachment body cavity drain or evacuation system.
It is a further object of some embodiments of this invention to provide a modular tap attachment.
It is a further object of some embodiments of this invention to provide lighter components which reverse their rotation and to reduce the number and weight of the components that reverse in the direction of their rotation.